Due to concerns about the depletion of oil resources and the increasing amount of carbon dioxide in the air causing global warming, a great deal of attention is now paid to biomass resources whose raw materials do not depend on oil and which materialize “carbon neutral” without increasing the amount of carbon dioxide when they are burnt. Even in the field of polymers, the development of biomass plastics produced from the biomass resources is actively under way. Since polylactic acid out of the biomass plastics has relatively high heat resistance and mechanical properties, its application is spreading to tableware, packaging materials and miscellaneous goods. Further, the possibility of using the biomass resources as industrial materials is now under study.
However, since polylactic acid has low hydrolysis resistance, the spread of its use to industrial materials such as electric/electronic parts and auto parts in which typical engineering plastics such as polycarbonate, polybutylene terephthalate and polyethylene terephthalate are used does not proceed.
Patent Document 1 proposes that an end-sealing agent is added to polylactic acid to seal at least part of the terminal carboxyl group of polylactic acid so as to suppress a reduction in strength by a hot water treatment. However, to use the polylactic acid as an industrial material, the level of its hydrolysis resistance is unsatisfactory.
Patent Document 2 proposes to improve the hydrolysis resistance of polylactic acid by mixing a carbodiimide compound and an antioxidant. This carbodiimide compound releases an isocyanate compound during a reaction for bonding to the end of a polyester, thereby producing a characteristic smell to worsen work environment.
Patent Document 3 discloses a macrocyclic carbodiimide compound. Since this compound is produced under high dilution, the concentration of the macrocyclic carbodiimide compound is low and it takes many days to react it with a polymer. Therefore, its utility as an end-sealing agent for polymers is low. Also, its efficiency as an end-sealing agent for polymers is low due to a high molecular weight for the carbodiimide group. Patent Document 3 does not take into consideration the reduction of an isocyanate gas smell produced by the end-sealing of a polymer. This macrocyclic carbodiimide compound has a long chain and is easily decomposed at a high temperature and unsuitable for use as an end-sealing agent for polymers having a high melting point, such as polyester.    (Patent Document 1) JP-A 2002-30208    (Patent Document 2) JP-A 2005-53870    (Patent Document 3) US Patent No. 2008/0161554